We have been investigating the importance of the cumulus to the interaction of macaque sperm and zonae pellucidae in the process of fertilization. We have developed an assay utilizing hamster cumulus and oocytes that determines the capability of macaque sperm to penetrate the cumulus. The assay has been validated with macaque cumulus recovered from superovulated animals after ultrasound-guided follicle aspiration. Non-activated sperm did not penetrate the cumulus, however large numbers of activated (with dbcAMP and caffeine) sperm penetrated the cumulus within 30 minutes. The cumulus contains high levels of hyaluronic acid (HA) which is produced by the cumulus cells surrounding mature oocytes and sperm produce hyaluronidase which is presumed to enhance sperm penetration of the cumulus by breaking down HA. To test this hypothesis, the effect of inhibiting hyaluronidase activity on the ability of sperm to penetrate the cumulus was investigated. Heparin and Apigenin are hyaluronidase inhibitors and both compounds significantly reduced the number of sperm that penetrated cumulus. We have also demonstrated that anti-PH20 IgG (antibodies to sperm hyaluronidase) will block cumulus penetration when sperm are preincubated in the IgG (4005g/ml). *KEY* Semen, Acrosome reaction, Reproduction, Contraception